Semiconductor device formed using a catalyst element capable of promoting crystallization

ABSTRACT

A semiconductor device using a crystalline semiconductor film is manufactured. The crystalline semiconductor film is formed by providing an amorphous silicon film with a catalyst metal for promoting a crystallization thereof and then heated for performing a thermal crystallization, following which the crystallized film is further exposed to a laser light for improving the crystallinity. The concentration of the catalyst metal in the semiconductor film and the location of the region to be added with the catalyst metal are so selected in order that a desired crystallinity and a desired crystal structure such as a vertical crystal growth or lateral crystal growth can be obtained. Further, active elements and driver elements of a circuit substrate for an active matrix type liquid crystal device are formed by such semiconductor devices having a desired crystallinity and crystal structure respectively.

This is a divisional application of Ser. No. 08/356,584, filed Dec. 15,1994.

FIELD OF THE INVENTION

The present invention relates to an active-matrix type liquid crystaldevice or thin film integrated circuit devices using a semiconductorlayer with crystallinity.

BACKGROUND OF THE INVENTION

Active-matrix type liquid crystal devices have been well known whichutilize thin film transistors (generally called as TFT). In aconventional active-matrix liquid crystal display device, a peripheralcircuit member is constituted by IC and is externally connected toterminals of matrix wirings of the pixels. Further, it is also known toform TFTs for forming a peripheral circuit on the same substrate onwhich TFTs are arranged in a matrix as a switching element in a pixelregion.

Since the TFTs formed on a peripheral circuit portion are to drive theTFTs formed in a matrix form on a pixel portion, they are required tohave a capability of passing a large amount of electric currenttherethrough. Specifically, they are required to have a large ON currentand a large mobility.

On the other hand, the TFTs formed on the pixel portion are not requiredto have a large mobility. Rather, they need to have a lower OFF current(leak current) in order to maintain electric charges on pixelelectrodes. Accordingly, the required characteristics for the TFTs of aperipheral circuit are different from those for the TFTs of a pixelportion.

Further, an amorphous silicon film has been used to form a TFT but itscharacteristics are not satisfactory. Therefore, a TFT using acrystalline silicon film has been investigated. Generally, it isnecessary to perform a thermal annealing at 600° C. or higher and formore than 24 hours for obtain a crystalline silicon film from anamorphous silicon film. However, a glass substrate which is usually usedas a substrate of a liquid crystal device can not endure such a thermalannealing because for example, a Corning 7059 glass has a distortionpoint of 593° C. In particular, one problem is that the glass substratetends to be distorted because of the high temperature so that it isdifficult to increase the size of the substrate.

The inventors of the present application have confirmed through theirexperiments that by contacting a slight amount of catalyst metal such asnickel or platinum with an amorphous silicon film, it is possible tocrystallize the silicon film at lower temperatures, for example, at 550°C. for about 4 hours. And the resultant crystallinity is comparable withthat obtained the above conventional thermal treatment at 600° C. Theinventors considered that these metal functions as a catalyst to promotethe crystallization of an amorphous silicon film.

The inventors also confirmed that there are two types of crystallizationin the case of using a catalyst as indicated below.

(1) A crystallization proceeds in a direction normal to a substrate in aregion where a catalyst was introduced.

(2) A crystallization proceeds in a direction parallel with a substratefrom a region to which a catalyst was introduced toward a region towhich a catalyst was not introduced.

The crystal structure in the case of (2) was confirmed by using a TEM(transmission type electron microscope) that columnar crystals grow in adirection parallel with a substrate. Also, the amount of nickelnecessary for causing the above first type of crystallization isdifferent from the amount of nickel necessary for causing the abovesecond type of crystallization. For example, when the (2) type ofcrystallization extends about 30 μm, the mount of the nickel necessaryto be introduced thereto is 10 times as much as that required in thecase of (1).

In the present specification, hereinbelow, the region where the above(1) type of crystallization occurs will be called as a vertical growthregion and the region where the above (2) type of crystallization occurswill be called as a lateral growth region.

SUMMARY OF THE INVENTION

It is an object of the present invention to form thin film transistorson a pixel region (pixel TFTs) and thin film transistors on a peripheralcircuit region on a same substrate through a simple process for anactive-matrix type liquid crystal device.

Moreover, it is another object of the present invention that, in anactive-matrix type liquid crystal device, pixel TFTs have a differentcrystallinity than TFTs formed on a peripheral circuit region.

In accordance with one aspect of the present invention, the method ofthe present invention includes a step of irradiating a laser light or alight having a sufficient strength on a selected portion of asemiconductor film to constitute a peripheral circuit region.

In accordance with another aspect of the invention, TFTs constituting aperipheral circuit are formed with a crystalline silicon film in whichcrystals grew in a direction approximately parallel with a directionalong which carriers of the TFTs flow while pixel TFTs are formed with acrystalline silicon film in which crystals grew in a directionapproximately perpendicularly with respect to a carrier direction of thepixel TFTs. The carrier direction means the direction along source anddrain regions of the TFT. Namely, when a carrier direction isapproximately aligned with a crystal growth direction, since carriersmove along the direction of grain boundaries, the influence of the grainboundaries with respect to the carrier flow is suppressed and thus sucha TFT can have a higher mobility. Accordingly, such a TFT is suitablefor forming a peripheral circuit which requires a higher ON current. Onthe other hand, when a carrier direction is perpendicular to a crystalgrowth direction, since carriers have to cross grain boundaries, the OFFcurrent can be decreased while the ON current is decreased. Accordingly,such a TFT is suitable as a pixel TFT for switching a pixel electrode inan electro-optical device.

It is still a further aspect of the present invention that TFTs having achannel region formed with a vertical growth silicon film (i.e. in whichcrystals grew perpendicularly to the substrate) and TFTs having achannel region formed with a lateral growth silicon (i.e. in whichcrystals grew horizontally with the substrate) are both formed on thesame substrate. Specifically, the TFTs associated with the verticalgrowth region is suitable as pixel TFTs for switching pixel electrodeswhile the TFTs associated with the lateral growth region is suitable asa peripheral circuit for driving the pixel TFTs. This feature is basedon the inventors' discovery that the amount of a catalyst required forforming a vertical growth film and that for forming a lateral growthfilm are different from each other. In order to accurately control theamount of a catalyst to be introduced into a semiconductor film, theinventors utilize a liquid for carrying a catalyst therein.

In accordance with the present invention the catalyst may be one or moreelements selected from the group consisting of Ni, Pd, Pt, Cu, Ag, Au,In, Sn, P, As and Sb. Alternatively, the catalyst may be one or moreelements selected from the group consisting of Group VIII elements,Group IIIb elements, Group IVb elements and Group Vb elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and features of the present inventionwill be explained in detail with reference to the attached drawings inwhich:

FIG. 1 shows a schematic diagram of an active-matrix type liquid crystaldevice in accordance with the present invention;

FIGS. 2A-2F show a manufacturing method of a thin film transistor for aperipheral circuit in accordance with Example 1 of the presentinvention;

FIGS. 3A-3F show a manufacturing method of a thin film transistor for apixel region in accordance with Example 1 of the present invention;

FIGS. 4A-4F show a manufacturing method of a thin film transistor for aperipheral circuit in accordance with Example 2 of the presentinvention;

FIGS. 5A-5F show a manufacturing method of a thin film transistor for apixel region in accordance with Example 2 of the present invention;

FIGS. 6A-6F show a manufacturing method of a thin film transistor for apixel region in accordance with Example 3 of the present invention;

FIGS. 7A-7F show a manufacturing method of a thin film transistor for aperipheral circuit in accordance with Example 3 of the presentinvention; and

FIG. 8 show a block diagram of an active matrix type liquid crystaldevice in accordance with Example 4 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a schematic diagram of a circuit substrate of an activematrix type liquid crystal device in accordance with the presentinvention. In FIG. 1, on a substrate 201, there are peripheral circuitregions (A) and (B), redundant peripheral circuit regions (A') and (B')which are used in case where the circuits (A) and (B) are defective.There is also a pixel region having a plurality of pixel TFTs arrangedin a matrix form on the same substrate for switching a plurality ofpixel electrodes.

In accordance with the preferred embodiments of the invention, acatalyst for promoting the crystallization of a semiconductor film isintroduced by a method in which a liquid carrying the catalyst thereinis used as explained below.

For preparing a liquid carrying the catalyst, it is possible to use apolar solvent selected from the group consisting of water, alcohol, acidand ammonium. Examples of nickel compounds which can be dissolved in apolar solvent are nickel bromide, nickel acetate, nickel oxalate, nickelcarbonate, nickel chloride, nickel iodide, nickel nitrate, nickelsulfate, nickel formate, nickel acetylacetonate, 4-cyclohexyl butyricacid, nickel oxide and nickel hydroxide.

Also, it is possible to use a non-polar solvent for dissolving a nickelcompound, for example, benzene, toluene, xylene, carbon tetrachloride,chloroform or ether. Examples of nickel compounds suitable for such asolvent are nickel acetyl acetonate and 2-ethyl hexanoic acid nickel.

Also, it is advantageous to add a surface activation agent to a catalystcontaining solution in order to improve the adhesivity of the catalystto the surface and control the adsorption property. The surfaceactivation agent may be applied directly onto the surface before coatingthe solution.

In the above mentioned solutions, nickel which is a catalyst element iscompletely dissolved in the solution. However, it is to be understoodthat nickel may not be completely dissolved in a solution. For example,it is possible to use a material like an emulsion in which nickel metalor nickel compound powders are uniformly dispersed. It is also possibleto use a solution which is for forming a silicon oxide film, forexample, OCD (Ohka Diffusion Source) which is supplied by Tokyo OhkaIndustry. In such a case. it is possible to form a silicon oxide filmwhich contains a catalyst therein by simply coating the solution andthen baking at 200° C. Desired impurities can be also added to thesolution.

The foregoing solutions are initially formed on an amorphous siliconfilm by a spin coating method and then dried so that a film containing acatalyst for promoting a crystallization of the silicon film is formed.

EXAMPLE 1!

This example relates to a manufacture of a circuit substrate of anactive matrix liquid crystal device as shown in FIG. 1 in accordancewith the above mentioned first aspect of the present invention.

FIGS. 2A-2F are cross sectional views for showing a manufacturing methodof a TFT in the peripheral circuit regions of FIG. 1. On the other hand,FIGS. 3A-3F are cross sectional views for showing a manufacturing methodof a TFT in the pixel region of FIG. 1. Therefore, FIGS. 2A-2F and FIGS.3A-3F correspond with each other and the both TFTs are formed on thesame substrate. It is to be understood that each step of FIGS. 2A-2F andFIGS. 3A-3F is carried out simultaneously. For example, the step of FIG.2A is simultaneously performed as the step of FIG. 3A. Also, the samereference number is used for showing a like element.

Initially, referring to FIGS. 2A and 3A, the substrate 201 is cleaned bywashing, following which a silicon oxide film 202 of 2000 Å thick isformed as a base layer by a plasma CVD using TEOS (tetra-ethoxy-silane)and oxygen as starting materials.

Then, an amorphous silicon film 203 of an intrinsic type is formed byplasma CVD to a thickness of 500-1500 Å, for example, 1000 Å. On theamorphous silicon film 203, a solution containing nickel as a catalyst,for example, a nickel acetate solution is formed by coating. Theconcentration of nickel in the solution is 10 ppm. Also, it isadvantageous to form a very thin oxide film on the amorphous siliconfilm before the formation of the nickel containing solution in order toimprove the wettability of the surface. The thickness of the oxide filmshould be several tens angstroms in order that nickel can penetratethrough it.

It should be noted that a plasma treatment, evaporation, sputtering orCVD may be used to form a nickel film or nickel containing film insteadof the above coating method.

After drying the coated solution 205, the silicon film 203 iscrystallized by a thermal annealing at a temperature of 500°-620° C.,for example, 550° C., for a period of 4 hours in a nitrogen atmosphere.During the annealing, nickel diffuses into the silicon film from thesurface and promotes the crystallization. The crystallization proceedsin a direction perpendicular to the substrate.

Referring to FIG. 2B, after the above crystallization, only the regionof the semiconductor film which corresponds to the peripheral circuitregion is irradiated with a laser light 216 in order to improve thecrystallinity. As a laser light, a KrF excimer laser (wavelength 248 nm,pulse width 20 nsec) is used with an energy density of 250 mJ/cm² and at2 shots/site. It is desirable to heat the substrate by another energysource to 400° C. during the laser irradiation in order to increase theeffect of the laser irradiation.

Also, other known lasers may be used instead of the excimer laser.Moreover, it is also possible to use an intense light instead of laser.For example, an infrared light of a wavelength of 1.2 μm may be used.The effect of the IR light irradiation is comparable with the effectobtainable with a heat annealing at a high temperature for severalminutes.

The concentration of nickel in the silicon film after thecrystallization is about 10¹⁸ atoms/cm³. Then, the silicon film 203 ispatterned by dry etching to form active regions 208 in an island form asshown in FIGS. 2C and 3C.

Thereafter, the surface of the active regions 208 is exposed to a 100volume % water vapor at a pressure of 10 atm and at a temperature of500°-600° C., typically, 550° C. for 1 hour in order to oxidize thesurface and form a silicon oxide film 209. The thickness of the siliconoxide film 209 is 1000 Å. After the oxidation, the substrate is thenexposed to an ammonium atmosphere (1 atm, 100%) at 400° C. At thiscondition, an infrared light having a peak at a wavelength of 0.6-4 μm,for example, 0.8-1.4 μm for 30-180 seconds is irradiated onto thesilicon oxide film 209 to perform a nitridation. It is possible to addHC1 at 0.1-10% to the atmosphere during this nitridation.

Subsequently, an aluminum film containing scandium at 0.01-0.2% isformed by sputtering to a thickness of 3000-8000 Å, e.g. 6000 Å and thenpatterned into a gate electrode 210.

Then, referring to FIGS. 2D and 3D, the surface of the aluminum gateelectrode is anodic oxidized to form an anodic oxide layer 211 of athickness of 2000 Å. The anodic oxidation is carried out within anethylene glycol solution in which a tartaric acid is contained at 1-5%.The thickness of the anodic oxide layer 211 will determine the thicknessof the offset gate area in the later step.

Referring then to FIGS. 2E and 3E, using the gate electrode 210 and thesurrounding anodic oxide film 211 as a mask, an N-type conductivityimpurity (phosphorous, here) is introduced into the active layer in aself-aligning manner by ion doping method (also called as plasma dopingmethod) in order to form impurity regions 212 and 213. Phosphine (PH₃)is used as a dopant gas. The acceleration voltage is 60-90 kV, forexample, 80 kV. The dose amount is 1×10¹⁵ -8×10¹⁵ cm⁻², for example,4×10¹⁵ cm⁻². As can be seen in the drawing, the impurity regions 212 and213 are offset from the gate electrode by a distance "x". Thisconfiguration is advantageous for reducing a leak current (off current)which occurs when applying a reverse bias voltage (i.e. a negativevoltage in the case of an NTFT) to the gate electrode. In particular,since it is desired that electric charges stored in a pixel electrode bemaintained without leaking in order to obtain an excellent display, theoffset configuration is particularly advantageous when the TFT is usedfor controlling a pixel of an active matrix.

Thereafter, an annealing is performed with a laser irradiation. As alaser, a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec.)or other lasers may be used. The conditions of the laser irradiation inthe case of KrF excimer laser are: energy density is 200-400 mJ/cm², forexample, 250 mJ/cm², a number of shots is 2-10 shots per one site, forexample, 2 shots. Preferably, the substrate is heated to 200°-450° C. toenhance the effect of the irradiation.

Referring to FIGS. 2F and 3F, an interlayer insulating film 214 ofsilicon oxide is formed through a plasma CVD to a thickness of 6000 Å.Further, a transparent polyimide film 215 is formed by spin coating toobtain a leveled surface. Then, in the pixel region, a transparentconductive film made of, for example, indium tin oxide is formed on theleveled surface and patterned into a pixel electrode 300 as shown inFIG. 3F. The ITO electrode will be connected to a terminal of a TFT as apixel electrode.

Then, the interlayer insulating films 214 and 215 are provided withcontact holes, through which electrode/wirings 217 and 218 are formed tocontact the impurity regions of the TFT. The electrode/wirings 217 and218 are formed of a metallic material, for example, a multi-layer oftitanium nitride and aluminum. As shown in FIG. 3F, one electrode 218 ofthe pixel TFT is connected to the pixel electrode 300 made of ITO.

Finally, an annealing in a hydrogen atmosphere of 1 atm is carried outat 350° C. for 30 minutes in order to complete a pixel circuit of anactive matrix circuit having TFTs.

EXAMPLE 2!

The present example relates to the second aspect of the presentinvention as mentioned before. Specifically, this example is directed toa manufacture of a circuit substrate for an electro-optical device ofthe same type shown in FIG. 1. In particular, the TFTs for both theperipheral circuit and the pixel circuit have their semiconductor layerin which crystals extend (grow) in a direction parallel with thesubstrate surface.

FIGS. 4A-4F are cross sectional views for showing a manufacturing methodof a TFT in peripheral circuit regions of FIG. 1 in accordance with thepresent example, while FIGS. 5A-5F are cross sectional views for showinga manufacturing method of a TFT in the pixel region of FIG. 1 inaccordance with the present example. Therefore, FIGS. 4A-4F and FIGS.5A-5F correspond with each other and the both TFTs are formed on thesame substrate. Also, the same reference number is used for showing alike element.

Initially, referring to FIGS. 4A and 5A, the substrate 201 is cleaned bywashing, following which a silicon oxide film 202 of 2000 Å thick isformed as a base layer by a plasma CVD using TEOS (tetra-ethoxy-silane)and oxygen as starting materials.

Then, an amorphous silicon film 203 of an intrinsic type is formed byplasma CVD to a thickness of 500-1500 Å, for example, 1000 Å.Subsequently, a silicon oxide film 225 of 500-2000 Å thick, for example,1000 Å is formed by plasma CVD. Then, the silicon oxide film 225 ispartly etched to form an exposed region 204 of the amorphous siliconfilm, which is to be provided with nickel in the later step.

Then, a solution containing nickel as a catalyst, for example, a nickelacetate solution is formed by coating. The concentration of nickel inthe solution is 100 ppm. Also, it is advantageous to form a very thinoxide film on the amorphous silicon film before the formation of thenickel containing solution in order to improve the wettability of thesurface. The thickness of the oxide film should be several tensangstroms or less in order that nickel can penetrate through it.

It should be noted that a plasma treatment, evaporation, sputtering orCVD may be used to form a nickel film or nickel containing film insteadof the above coating method.

After drying the coated solution, the silicon film 203 is crystallizedby thermal annealing at a temperature of 500°-620° C., for example, 550°C., for 4 hours in a nitrogen atmosphere. The crystallization starts atthe region 204 of the silicon film to which nickel is directlyintroduced and it proceeds to adjacent regions in a direction parallelwith the substrate surface as shown by. an arrow in the FIGURE.Accordingly, there is formed a crystalline silicon film in whichcrystals grow parallel with the substrate below the silicon oxide film225. The length of the lateral growth region is about 25 μm. Also, thedirection of the crystal growth in the lateral growth region isapproximately aligned with the <111> axis of the crystal.

Referring to FIG. 4B, after the above crystallization, the semiconductorfilm only in the peripheral circuit region is irradiated with a laserlight 216 in order to improve the crystallinity thereof. As a laserlight, a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) isused with an energy density of 250 mJ/cm² and at 2 shots/site. It isdesirable to heat the substrate by another energy source to 400° C.during the laser irradiation in order to increase the effect of thelaser irradiation.

Also, another kind of laser may be used instead of an excimer laser.Moreover, it is possible to use an intense light instead of laser. Forexample, an infrared light of a wavelength of 1.2 μm may be used.

Then, the silicon oxide film 205 is removed by etching. At the sametime, the thin oxide film formed on the region 204 is also removed.Further, the silicon film 203 is patterned by dry etching in order toform active regions 208 in the form of islands. The region 204 wasdirectly introduced with nickel so that the concentration of the nickelin this region is higher. Also, the end portion 227 of crystal growthcontains nickel at a higher concentration. On the other hand, the region208 contains nickel at a lower concentration than the regions 204 and227. Accordingly, the patterning of the silicon film is performed insuch a manner that the silicon island 208 (active region) does notoverlap with the high concentration regions 204 or 227.

Thereafter, the surface of the active regions 208 is exposed to a 100volume % water vapor at a pressure of 10 atm and at a temperature of500°-600° C., typically, 550° C. for 1 hour in order to oxidize thesurface and form a silicon oxide film 209 as shown in FIGS. 4C and 5C.The thickness of the silicon oxide film 209 is 1000 Å. After theoxidation, the substrate is exposed to an ammonium atmosphere (1 atm,100%) at 400° C. At this condition, an infrared light having a peak at awavelength of 0.6-4 μm, for example, 0.8-1.4 μm for 30-180 seconds isirradiated onto the silicon oxide film 209 to perform a nitridation. HC1may be added at 0.1-10% to the atmosphere during this nitridation.

Subsequently, an aluminum film containing scandium at 0.01-0.2% isformed by sputtering to a thickness of 3000-8000 Å, for example, 6000 Åand then patterned into a gate electrode 210.

Then, referring to FIGS. 4D and 5D, the surface of the aluminum gateelectrode is anodic oxidized to form an anodic oxide layer 211 of athickness of 2000 Å. The anodic oxidation is carried out within anethylene glycol solution in which a tartaric acid is contained at 1-5%.The thickness of the anodic oxide layer 211 will determine the thicknessof the offset gate area in the subsequent impurity introducing step byion doping.

Referring then to FIGS. 4E and 5E, using the gate electrode 210 and thesurrounding anodic oxide film 211 as a mask, an N-type conductivityimpurity (phosphorous, here) is introduced into the active layer in aselfaligning manner by ion doping method (also called as plasma dopingmethod) in order to form impurity regions 212 and 213 as source anddrain regions. Phosphine (PH₃) is used as a dopant gas. The accelerationvoltage is 60-90 kV, for example, 80 kV. The dose amount is 1×10¹⁵-8×10¹⁵ cm⁻², for example, 4×10¹⁵ cm⁻². As can be seen in the drawing,the impurity regions 212 and 213 are offset from the gate electrode by adistance "x". This configuration is advantageous for reducing a leakcurrent (off current) which occurs when applying a reverse bias voltage(i.e. a negative voltage in the case of an NTFT) to the gate electrode.In particular, since it is desired that electric charges stored in apixel electrode be maintained without leaking in order to obtain anexcellent display, the offset configuration is particularly advantageouswhen the TFT is used for controlling a pixel of an active matrix.

Thereafter, an annealing is performed with a laser irradiation. As alaser, a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec.)or other lasers may be used. The conditions of the laser irradiation inthe case of KrF excimer laser are: energy density is 200-400 mJ/cm², forexample, 250 mJ/cm², a number of shots is 2-10 shots per one site, forexample, 2 shots. Preferably, the substrate is heated to 200°-450° C. toenhance the effect of the irradiation.

Referring to FIGS. 4F and 5F, an interlayer insulating film 214 ofsilicon oxide is formed through a plasma CVD to a thickness of 6000 Å.Further, a transparent polyimide film 215 is formed by spin coating toobtain a leveled surface. Then, a transparent conductive film made of,for example, indium tin oxide is formed on the leveled surface andpatterned into a pixel electrode 300 as shown in FIG. 5F. The ITOelectrode will be connected to a terminal of a TFT as a pixel electrodein the pixel region.

Then, the interlayer insulating films 214 and 215 are provided withcontact holes, through which electrode/wirings 217 and 218 are formed tocontact the impurity regions of the TFT. The electrode/wirings 217 and218 are formed of a metallic material, for example, a multi-layer oftitanium nitride and aluminum. As shown in FIG. 5F, one electrode 218 ofthe pixel TFT is connected to the pixel electrode 300 made of ITO.

Finally, an annealing in a hydrogen atmosphere of 1 atm is carried outat 350° C. for 30 minutes in order to complete a pixel circuit of anactive matrix circuit having TFTs.

As a modification of the second example, it is advantageous to arrangethe TFTs of the pixel region shown in FIG. 5F in such a manner that thedirection of crystal growth is approximately orthogonal to the directionof the carrier flow of the TFT. Thereby, it is possible to minimize anOFF current when the TFT is in its OFF condition because the carriersmust pass across grain boundaries. On the other hand, the TFTs of aperipheral circuit shown in FIG. 4F are arranged so that the directionof the carrier flow is aligned with the direction of the crystal growth.Accordingly, the carriers flow along grain boundaries and it is possibleto increase the mobility. In order to achieve such a configuration,during the manufacture of the pixel TFTs shown in FIGS. 5A-5F, nickelshould be introduced into a region of the silicon film, which is infront of the TFT or behind the TFT in the drawing sheet. By doing so,the crystals laterally grow in a direction which is perpendicular to thedirection along source and drain regions 212 and 213, resulting in thatthe carriers pass across grain boundaries. Other manufacturingconditions may be entirely the same as those explained before.

EXAMPLE 3!

The present example is directed to a manufacture of an active matrixliquid crystal device as shown in FIG. 1. In the device of the presentexample, the TFTs of the pixel region are formed with a crystallinesilicon film in which crystals grew in a direction perpendicular to thesubstrate surface while the TFTs of the peripheral circuit (also calledas driver TFTs) are formed with a crystalline silicon film in whichcrystals grew in a direction parallel with the substrate surface.Therefore, the present example is characterized in that crystal growthsof the pixel TFTs and the driver TFTs occur in different ways from eachother.

The silicon film for forming the pixel TFTs will be directly added inits hole area with a catalyst material for promoting a crystallizationthereof and then thermally crystallized.

Also, the silicon film for forming the driver TFTs will be crystallizedby introducing a catalyst into a first region and then thermallyannealed in order that the crystals grow from the first region toward asecond region adjacent thereto horizontally with respect to thesubstrate.

In accordance with the present example, the amount of the catalystelement introduced into the foregoing regions is varied in each region.This is because the crystal structure of the obtained film depends uponthe amount of the catalyst element. However, the concentration of thecatalyst element in the active regions can be made almost the samebecause the concentration of the catalyst element in the lateral growthregion is smaller than that in the region to which the catalyst elementis directly introduced.

FIGS. 6A-6F are cross sectional views for showing a manufacturing methodof a TFT in the pixel region of FIG. 1 in accordance with the presentexample, while FIGS. 7A-7F are cross sectional views for showing amanufacturing method of a TFT in the peripheral circuit regions of FIG.1 in accordance with the present example. Therefore, FIGS. 6A-6F andFIGS. 7A-7F correspond with each other and the both TFTs are formed onthe same substrate.

Referring to FIGS. 6A and 7A, a surface of a substrate 201 is cleaned bya proper cleaning method and a silicon oxide film 202 is formed on thecleaned surface to a thickness of 2000 Å by plasma CVD using TEOS andoxygen as starting gases. Then, an intrinsic (i-type) amorphous siliconfilm 203 is formed by plasma CVD or LPCVD to a thickness of 500-1500 Å,for example, 1000 Å. Subsequently, a silicon oxide film 225 is formed byplasma CVD to a thickness of 500-2000 Å, for example, 1000 Å. The oxidefilm 225 is selectively etched in order that only the pixel region ofthe amorphous silicon film 203 is exposed. Therefore, the peripheralcircuit region of the silicon film remains covered with the oxide film225 which functions as a mask in the later step.

Then, an extremely thin oxide film (e.g. several tens Å thick) is formedon the exposed surface of the amorphous silicon film 203. This extremelythin oxide film improves the wetting property of the surface withrespect to a solution which will be applied later. The oxide film may beformed by thermal oxidation, or a UV irradiation in an oxygen gas.

Thereafter, an acetic acid salt solution 205 which contain nickel isapplied onto the entire surface by coating in order that the exposedsurfaces of the amorphous silicon film are provided with nickel. Thevolume concentration of nickel in the acetate solution is 10 ppm.

After the coating, the substrate is heat treated at 200 -500° C., forexample, 300° C. so that nickel silicide is formed on the surface of theamorphous silicon film which is directly provided with the acetic acidsalt solution. Accordingly, only the pixel region of the silicon film isprovided with the nickel silicide while the peripheral circuit region ofthe silicon film is not provided with nickel silicide because of theexistence of the mask made of the silicon oxide film 225.

Then, referring to FIG. 7B, the silicon oxide film 225 used as a mask isremoved and another silicon oxide film 225' is formed on the entiresurface. The formation of the silicon oxide film may be done in the samemanner as the formation of the oxide film 225. The silicon oxide film225' is patterned to expose only a portion of the silicon film as shownin FIG. 7B. On the other hand, the silicon film 203 on the pixel regionis completely covered with the silicon oxide film 225'.

In the above condition, an acetic acid salt solution 205' which containsnickel as a crystallization promoting catalyst is coated onto the entiresurface. Therefore, only the exposed region of the silicon film isprovided with the nickel. The volume concentration of the nickel in thesolution is 100 ppm. Accordingly, the amount of nickel added to thesilicon film is 10 times as high as the amount of nickel added to thesilicon film in the former step as shown in FIG. 6A.

Thereafter, the substrate is heat treated at 200-500° C., for example,300° C. in order to form nickel silicide on the exposed region 204 ofthe silicon film in FIG. 7B.

By the foregoing steps, the peripheral circuit region of the amorphoussilicon film is provided with nickel at a concentration 10 times as highas the region of the amorphous silicon film in the pixel region.

The silicon film 203 provided with the catalyst for promoting thecrystallization thereof is then crystallized by thermal annealing in anitrogen gas at 500°-620° C. for example at 550° C. for 4 hours. Thecrystallization proceeds in a different manner in the pixel region andthe peripheral circuit region. That is, in the pixel region of thesilicon film as shown in FIG. 6A, the crystal growth occursperpendicularly to the substrate because the entire surface of thesilicon film is provided with nickel. On the other hand, in theperipheral circuit region as shown in FIG. 7B, since the region 204 isselectively provided with nickel, the crystallization proceeds from theregion 204 to a region 228 adjacent thereto in a lateral direction. Thecrystallization of the former type is called a vertical growth and thelatter is called a lateral growth as said before.

The length of the lateral growth is about 30 μm. This can be increasedby increasing the amount of the added nickel, by elevating thetemperature of the thermal annealing and/or by increasing the time ofthe thermal annealing. Also, it was confirmed that the lateral crystalgrowth direction in the region 228 is aligned with the <111> axis of thecrystal.

The concentration of nickel in the silicon film is 1×10¹⁸ atoms/cm³ atthe pixel region of FIG. 6B, and 1×10¹⁹ atoms/cm³ at the region 204 ofFIG. 7B, and 1×10¹⁸ atoms/cm³ at the region 228. Accordingly, the nickelconcentration in active regions of TFTs for both of the peripheralcircuit region and the pixel region is controlled to be 1×10¹⁸atoms/cm³. Of course, it is possible to control the nickel concentrationby changing the amount of nickel to be added. For example, when thecrystallinity of the semiconductor film in the pixel region may belowered, the nickel concentration in the solution 205 may be lowered.Also, when it is desired to increase the crystal growth length in FIG.7B, the nickel concentration in the acetic acid salt solution 205'should be increased.

It is desirable to irradiate the semiconductor film with intense lightfor improving the crystallinity after the above crystallization. Aninfrared light having a wavelength of 1.2 μm or laser light may be usedas a light source. Also, it is appropriate to irradiate only theperipheral circuit region with light in the same manner as in the firstexample of the present invention.

After the crystallization step, the silicon oxide film 225' is removedby etching and then the silicon film 203 is patterned by dry etching inorder to form active regions 300 and 301 in the form of an island. InFIG. 6C, the active region 300 comprises the crystalline silicon inwhich crystals grew in a direction vertical to the substrate. Also, inFIG. 7C, the active region 301 comprises the crystalline silicon film inwhich crystals grew from the region 204 in a lateral direction.

The region 204 was directly introduced with nickel so that theconcentration of the nickel in this region is higher. Also, the region227 which is a top end of crystal growth also contains nickel at ahigher concentration. Accordingly, the patterning of the silicon film isperformed in such a manner that the active region does not overlap withthe high concentration regions 204 and 227.

After the patterning, a silicon oxide film 209 of 1000 Å thick is formedby LPCVD as a gate insulating film. Subsequently, an aluminum filmcontaining scandium 0.01 to 0.2% is deposited to 3000-8000 Å thick, forexample, 6000 Å thick by sputtering, and then patterned into a gateelectrode 210. (FIGS. 6C and 7C)

Then, referring to FIGS. 6D and 7D, the surface of the aluminum gateelectrode is anodic oxidized to form an anodic oxide layer 211 of athickness of 2000 Å. The anodic oxidation is carried out within anethylene glycol solution in which a tartaric acid is contained at 1-5%.The thickness of the anodic oxide layer 211 will determine the thicknessof the offset gate area in the subsequent impurity introducing step byion doping.

Referring then to FIGS. 6E and 7E, using the gate electrode 210 and thesurrounding anodic oxide film 211 as a mask, an N-type conductivityimpurity (phosphorous, for example) is introduced into the active layerin a self-aligning manner by ion doping method in order to form impurityregions 212 and 213 as source and drain regions. Phosphine (PH₃) is usedas a dopant gas. The acceleration voltage is 60-90 kV, for example, 80kV. The dose amount is 1×10¹⁵ -8×10¹⁵ cm⁻², for example, 4×10¹⁵ cm⁻². Ascan be seen in the drawing, the impurity regions 212 and 213 are offsetfrom the gate electrode by a distance "x". This configuration isadvantageous for reducing a leak current (off current) which occurs whenapplying a reverse bias voltage (i.e. a negative voltage in the case ofan NTFT) to the gate electrode. In particular, it is advantageous toprovide an offset region in the TFT for the pixel region in order toprevent charges applied to a pixel electrode from leaking.

Also, when forming a CMOS structure for the peripheral circuit, it isnecessary to introduce a P-type impurity as a dopant. In such a case, amask may be used so that the ion doping can be selectively performed.

Thereafter, an annealing is performed with a laser irradiation. As alaser, a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec.)or other lasers may be used. The conditions of the laser irradiation inthe case of KrF excimer laser are: energy density is 200 -400 mJ/cm²,for example, 250 mJ/cm², a number of shots is 2-10 shots per one site,for example, 2 shots. Preferably, the substrate is heated to 200°-450°C. to enhance the effect of the irradiation.

Referring to FIGS. 6F and 7F, an interlayer insulating film 214 ofsilicon oxide is formed through a plasma CVD to a thickness of 6000 Å.Further, a transparent polyimide film 215 is formed by spin coating toobtain a leveled surface. Then, a transparent conductive film made of,for example, indium tin oxide is formed on the leveled surface andpatterned into a pixel electrode 300 as shown in FIG. 6F.

Then, the interlayer insulating films 214 and 215 are provided withcontact holes, through which electrode/wirings 217 and 218 are formed tocontact the impurity regions of the TFT. The electrode/wirings 217 and218 are formed of a metallic material, for example, a multi-layer oftitanium nitride and aluminum. As shown in FIG. 6F, one electrode 218 ofthe pixel TFT is connected to the pixel electrode 300 made of ITO.

Finally, an annealing in a hydrogen atmosphere of 1 atm is carried outat 350° C. for 30 minutes in order to complete the TFTs for the activematrix and the peripheral circuit of a liquid crystal device.

The TFT shown in FIG. 6F utilizes the vertical growth silicon film sothat the carriers must pass across grain boundaries. Therefore, themobility and the ON current is relatively small because of the influenceof the grain boundaries. However, the OFF current can be reduced.

Also, the TFT shown in FIG. 7F utilizes the lateral growth silicon filmso that carriers flow in a direction approximately parallel with thecrystal growth direction. Therefore, the influence of the grainboundaries can be reduced and the ON current is increased.

EXAMPLE 4!

In this example, an integrated circuit is to be formed on one glasssubstrate by mounting thereon a display, CPU, memory etc by employingthe third aspect of the invention in which a desired crystallinestructure or crystal structure (lateral growth or vertical growth) maybe obtained in a desired region.

FIG. 8 shows a block diagram of an electro-optic (device). In thediagram, the input port is to read a signal input from an outside and toconvert it into a display signal, and the correction memory is peculiarto each panel, which corrects the input signal or the like in accordancewith a specific characteristics of an active matrix panel. Inparticular, the correction memory uses a non-volatile memory in which aninformation of each pixel is stored in order to perform the correctionat each pixel. That is, if there is a defective pixel (point defect) inthe electro-optical device, pixels surrounding the defective pixel aresupplied with signals which are corrected in order to disappear or coverthe defect pixel. Also, when there is a pixel of which brightness islower than others, the signal to be applied to that pixel is correctedto be a larger signal, thereby, the brightness of that pixel becomes thesame as its surrounding pixels.

The CPU and the memory are equivalent to those used in a conventionalcomputer. Especially, the memory uses a RAM in which an image memorycorresponding to each pixel is stored. Also, it has a function ofchanging an intensity of back light on the rear side of the substrate inresponse to the image information.

The reference numeral 74 shows a region on which a decoder/drivercircuit which is a peripheral circuit is formed. 71 shows an activematrix TFT, 72 shows a capacitor, and 73 shows a liquid crystal. In thisexample, the foregoing circuits are formed on one substrate. And, acrystalline silicon film is selectively formed depending upon therequired crystallinity or crystal structure.

While various examples have been disclosed, it is to be understood thatthe scope of the present invention should not be limited to thoseparticular examples. Many modifications may be made without departingthe scope of the invention. For example, while film transistors aremainly discussed, it is possible to form other types of a semiconductordevice in accordance with the present invention, for example, a diode,photoelectric conversion device, etc. Also, the present invention iseffective for the use of other catalyst materials in place of nickel.Furthermore, the catalyst may be first formed over a substrate and thena semiconductor film may be formed thereon.

What is claimed is:
 1. A semiconductor device comprising at least firstand second thin film transistors formed over a substrate, each of saidthin film transistors having a crystalline semiconductor film added witha catalyst for promoting a crystallization thereof, wherein aconcentration of said catalyst in the semiconductor film of said firstthin film transistor is different from that in the semiconductor film ofthe second thin film transistor.
 2. The device of claim 1 wherein saidcatalyst comprises metal selected from the group consisting of Ni, Pd,Pt, Cu, Ag, Au, In, Sn, P, As and Sb.
 3. The device of claim 1 whereinsaid catalyst comprises a material selected from Groups VIII, IIIb, IVband Vb elements.
 4. A semiconductor device comprising at least first andsecond thin film transistors formed over a substrate, each of said thinfilm transistors having a crystalline semiconductor film added with acatalyst for promoting a crystallization thereof,wherein a concentrationof said catalyst in the semiconductor film of said first thin filmtransistor is different from that in the semiconductor film of thesecond thin film transistor, and wherein the semiconductor film of saidfirst transistor has crystals extending in a direction perpendicular tothe substrate while the semiconductor film of said second transistor hascrystals extending in a direction parallel with the substrate.
 5. Thedevice of claim 4 wherein said catalyst comprises metal selected fromthe group consisting of Ni, Pd, Pt, Cu, Ag, Au, In, Sn, P, As and Sb. 6.The device of claim 4 wherein said catalyst comprises a materialselected from Groups VIII, IIIb, IVb and Vb elements.
 7. Anelectro-optical device comprising:a substrate having an insulatedsurface; a peripheral circuit region having a first thin film transistorformed over said substrate, wherein said thin film transistor has acrystalline semiconductor film added with a catalyst for promoting acrystallization of said semiconductor film at a first concentration; anda pixel circuit region having a second thin film transistor formed oversaid substrate, wherein said thin film transistor has a crystallinesemiconductor film added with a catalyst for promoting a crystallizationof said semiconductor film at a second concentration which is differentfrom said first concentration.
 8. The electro-optical device of claim 7wherein said first concentration is larger than said secondconcentration.
 9. The electro-optical device of claim 7 wherein thecrystalline semiconductor film of said first transistor has a highercrystallinity than that of said second transistor.
 10. Theelectro-optical device of claim 7 wherein the crystalline semiconductorfilm of said first transistor has crystal grains extending verticallywith respect to the surface of substrate.
 11. The electro-optical deviceof claim 7 wherein the crystalline semiconductor film of said secondthin film transistor has crystal grains extending parallel with respectto the surface of the substrate.
 12. The electro-optical device of claim7 wherein the crystalline semiconductor film of said first thin filmtransistor has crystal grains extending vertically with respect to adirection along which carriers of the first transistor flow.
 13. Theelectro-optical device of claim 7 wherein the crystalline semiconductorfilm of said second thin film transistor has crystal grains extendingalong a direction in which carriers of the second transistor flow. 14.An active matrix display device comprising:a plurality of first thinfilm transistors arranged in a matrix form and formed on a substrate;and a driving circuit comprising second thin film transistors formed onsaid substrate, said driving circuit including at least one of acorrection memory, an input-port, a memory and a CPU, wherein a channelregion in both of said first and second thin film transistors comprisesa crystallized semiconductor added with a catalyst element, which iscapable of promoting crystallization of silicon.
 15. The display deviceof claim 14 wherein said driving circuit further includes a shiftregister or a decoder.
 16. An active matrix display device comprising: aplurality of first thin film transistors arranged in a matrix form andformed on a substrate; anda driving circuit comprising second thin filmtransistors formed on said substrate, said driving circuit including atleast one of a correction memory, an input-port, a memory and a CPU,wherein a channel region in both of said first and second thin filmtransistors comprises a crystallized semiconductor added with a catalystelement, which is capable of promoting crystallization of silicon, andwherein the channel region in the second thin film transistor has acrystalline structure in which crystals extend in a direction parallelwith a surface of said substrate.
 17. An active matrix display devicecomprising:a plurality of first thin film transistors arranged in amatrix form and formed on a substrate; and a driving circuit comprisingsecond thin film transistors formed on said substrate, said drivingcircuit including at least one of a correction memory, an input-port, amemory and a CPU, wherein a channel region in both of said first andsecond thin film transistors comprises a crystallized semiconductoradded with a catalyst element, which is capable of promotingcrystallization of silicon, and wherein the channel region in the secondthin film transistor has a crystalline structure in which crystalsextend in a direction perpendicular to a surface of said substrate.